HIV is primarily sexually transmitted with young women bearing a disproportionate burden of disease. Thus, in the absence of an effective vaccine, there is an urgent need for safe and effective pre-exposure prophylaxis (PrEP). We hypothesize that the optimal strategy will combine potent drugs that are active in multiple anatomic compartments, exhibit rapid and sustained pharmacokinetics (PK), and are safe. Ideally, sustained delivery formulations should be prioritized, as adherence to daily or coitally dependent dosing has proven difficult. Building from these concepts, this Program will focus on intravaginal ring (IVR) delivery of tenofovir (TFV) prodrugs, tenofovir disoproxil fumarate (TDF) or GS7340 in combination with maraviroc (MVC), a licensed CCR5 entry inhibitor, or IQP-0528, a potent non-nucleoside reverse transcriptase and entry inhibitor. We have successfully delivered TDF and IQP-0528 from IVRs in pig-tailed macaques (PTM) and will explore vaginal delivery of the alternative TFV prodrug, GS7340, because it has greater antiviral activity than TFV, better distribution into lymphoid tissues and may be more stable than TDF. TDF will be the primary agent of study because of its greater tissue permeability and potency compared to TFV, excellent safety profile and our exciting progress with reservoir-based IVR TDF delivery in PTMs. The conflicting results of recent clinical trials with oral and vaginal PrEP highlight the difficulties and complexities in translating preclinical data into real world use. Behavior and adherence likely contribute to the variable trial results. However, we propose that there is also a biological basis for these disparate outcomes. We hypothesize that the female genital tract mucosal environment, which may differ in adolescents compared to hormonally mature women, is altered in response to sex, hormonal contraception, and bacterial vaginosis (BV). These changes modulate drug PK and pharmacodynamics (PD), as well as the risk of HIV infection, to shift the balance from protection to infection. We will test this paradigm with clinical samples obtained from U.S. and African adult or adolescent subjects pre- and post-sex, prior to and after initiating depot medroxyprogesterone (DMPA) contraception, and before and after successful treatment of BV for their impact on PK/PD and HIV susceptibility ex vivo using novel cell and tissue culture models. We will evaluate the impact of the clinical samples on drug permeability, uptake, metabolism, and antiviral activity and explore the mechanisms that contribute to observed changes. Results will promote the identification of optimal formulations and identify new strategies for HIV prevention.